|A successful earth construction project starts with proper foundations. The rammed earth walls need to be placed and supported upon engineered concrete footings. Vertical reinforcing steel extends from these footings through the earth wall into the bond beam at the top of the wall. Conventional concrete slab or strip footings are generally used, the size and shape of which is subject to soil conditions.
||Rammed earth walls are constructed by ramming a mixture of selected aggregates, including gravel, sand, silt and clay into a structural arrangement called the form.
The custom form work is then placed and secured in sections ready for the earth. This requires plywood sheets, timber planks and concrete construction bolts not too dissimilar to in-situ concrete construction but with its own specific requirements.
Adding the Earth
A desired soil is tested for suitability, mixed with approximately 7-10% cement and then placed and compacted into the formwork in layers of between 150mm and 200mm deep. Using a pneumatic rammer the soil is pounded down to approximately 5/8ths of the loose height of the material. Walls are rammed into layers of approximately 100mm. The form work is removed immediately after compacting to reveal the finished surface of the walls. Once all the walls have been completed a concrete bond beam is cast, linking the top of the walls together.
Joints and Connections
Walls are built in panels of approximately 2 metres in length. When a length of wall consists of more than one panel a rebate is built into the end of the first wall. The second wall then moulds into this to lock the walls together for lateral stability. This connection is what we call a 'Control Joint'.
Openings can be made, without concrete lintels, with spans of up to 2 metres in rammed earth walls (subject to strength and engineering requirements). Specialised formwork can be made to make features like arches, reliefs, stencils and curved walls and the formwork can often be reused.
Mostly, however, openings are spanned with concrete lintels or bond beams. We have spanned openings in this way of up to 6m; such as a garage door opening or for a large joinery unit (window/door) on the north face of a dwelling.
Timber Framing and Finish Work
Once the earth walls and concrete work are completed, the timber-framing phase of the project begins. This includes roof, some interior walls and for 2 storey or more homes, mid floor framing if suspended concrete slabs are not used.
Most conventional masonry fixings work with rammed earth walls, although they usually need to be set in at about one and a half times the depth normally used for fixings into concrete.
The off-form finish of stabilised rammed earth generally requires no additional finish. Rammed earth should be protected by eaves, overhangs or a breathing type sealer if exposed to severe weather conditions. Walls can be surface textured to create different finishes. They can also be very easily rendered, plastered or painted.
Mostly the walls are left in their natural state.